Multiple orientation magnetic information storage

ABSTRACT

A system for transferring information to and from a magnetic disk is disclosed wherein the information may be encoded on a data track in a large number of polarization orientations in comparison to conventional bidirectional recording schemes. In one embodiment of the present invention, it is contemplated that a single segment may be polarized in eight different orientations, each of which being distinguishable from each other by a read/write head. Polarization of a segment in one of eight different orientations significantly increases the amount of information which can be stored in any given segment relative to conventional systems which are polarized in only one of two orientations. Thus, the amount of information which may be stored on a disk may be increased without having to alter the linear or radial density of the disk.

CLAIM OF PRIORITY

[0001] This application is a continuation of U.S. patent applicationSer. No. 09/326,155, entitled “Multilevel Orientation MagneticInformation Storage,” filed Jun. 4, 1999 which claims priority to U.S.Provisional Application No. 60/088,052 filed on Jun. 4, 1998.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to a method of storing andretrieving data to and from a magnetic disk, and in particular to amethod of storing and retrieving data to and from a magnetic diskwherein data may be encoded on a data track in a large number ofpolarization orientations in comparison to conventional bidirectionalrecording schemes.

[0004] 2. Description of Related Art

[0005] Current data storage systems, such as those in computer hard diskdrives, employ magnetic, optical or magneto-optical heads for recordingand retrieving data to and from magnetic storage disks. Magnetic headsmay include a transducer element for reading and writing the data and anair-bearing slider which supports the transducer over the disk. Atpresent, there are three widely used head technologies in disk drives:ferrite metal in gap (MIG) technology, which uses machined ferriteceramic cores with wire coils; inductive thin film technology; andmagnetoresistive (MR) technology.

[0006] The principal elements of an inductive magnetic recording headare a magnetic core including two poles separated by a non-magnetic gap,and an electrically conductive coil wrapped or deposited in turns aroundthe core. Data is transferred between the head and a magnetic storagedisk in concentric data tracks having a radial width on the order of afew microns or less. Each track is divided into a plurality of sectorsonto which the desired data is magnetically encoded. The radial trackdensity of a given storage medium is described as a number of tracks perinch (TPI). Linear density may be described as a number of bits per inch(BPI) within a given track.

[0007] To write data to a particular sector, a current is passed throughthe coil, thereby inducing a magnetic field in the core. The magneticfield fringes out across the gap in arcuate flux lines and, in so doing,passes into the disk to magnetize a segment of the disk. Reversing thedirection of the current reverses the polarity of the next magnetizedsegment as it passes by the gap of the head. Thus, referring to FIGS. 1and 2, as the magnetic disk rotates under the head, data is laid down ondata tracks 20 in segments 22 of alternating magnetic polarities(indicated by oppositely facing arrows). Conventional recording systemsof this kind are referred to as longitudinal recording systems, assegments on a data track are oriented either to the left (i.e.,up-track) or to the right (i.e., down-track) in the plane of the disk.Alternatively, in perpendicular recording systems, it is known toprovide the recording medium with an easy axis of magnetizationperpendicular to the plane of the disk. Systems of this kind utilize adifferent transducer element and result in segments on a data trackbeing oriented into and out of the plane of the disk.

[0008] To read data, the previously encoded disk is again passed by thehead and the reversing magnetic polarities within the segments inducereversing magnetic fields in the core. These reversing magnetic fieldsin the core generate correspondingly reversing currents in the coil,which are sensed and decoded into binary numbers by the drive circuitry.In contrast to an inductive disk head, which is typically designed toread and write data using a single inductive element, an MR disk headuses an inductive element to write data onto the disk and a separate MRelement to read data from the disk. The MR read element incorporates amagnetoresistor whose electrical resistance changes in the presence of amagnetic field. As the encoded disk is passed by the read element, thedisk drive circuitry senses and decodes the changes in electricalresistance caused by the reversing magnetic polarities.

[0009] There is a constant effort in the contemporary computer field toincrease the amount of information that can be stored on a magnetic diskof given size. Conventionally, this problem has been attacked by writingdata in smaller segments, to thus increase linear density, and/or bydecreasing the width of a data track to increase radial density.

[0010] One method which has proved successful in increasing radialdensity in the magnetic tape recording industry is azimuth recording. Asshown in U.S. Pat. No. 4,539,615 to Arai et al., azimuth recordingutilizes “odd” and “even” transducer elements for recording “odd” and“even” data tracks, respectively, on the storage medium. In particular,as shown in FIG. 2, the gap in the odd transducer element is slanted ina first direction so as to polarize segments on one data track in afirst slanted direction, and the gap in the even transducer element isslanted in a second direction so as to polarize segments on an adjacentdata track in a second slanted direction. During the reading process,the even transducer element is insensitive to data on the odd datatracks, and the odd transducer element is insensitive to data on theeven data tracks. In this way, the odd and even data tracks may beplaced close together without a danger that data written on one trackwill be partially picked up by the neighboring track.

[0011] While conventional systems have attempted to increase the amountof information stored on a disk by increasing linear and radialdensities, the amount of information contained in any given segment hasremained unchanged. All conventional recording schemes store only asingle bit (i.e., either a “0” or a “1”) in a particular segment, whichstate is indicated by the direction of polarization of that segment.Therefore, the amount of information which is stored into and read froma particular segment is limited to only one of two possible states.

[0012] Moreover, recording data onto segments by polarizing respectivesegments in completely opposite directions results in certaindisadvantages at the boundary, or transition, between adjacent segments.While adjacent segments are typically illustrated, as in FIGS. 1 and 2,to have a sharp transition from one polarity to the opposite, thetransition in fact takes place gradually as shown in the enlarged viewof the boundary region shown in FIG. 3. When the magnetic field acrossthe gap reverses completely from one direction to the oppositedirection, there will be relatively large boundary, or transition lengthL₁, which includes individual domains 24 oriented in both directions atthe boundary reverse their direction gradually. The relatively largetransition length L₁ makes it more difficult to increase the lineardensity within a data track.

[0013] A further disadvantage to polarizing segments in oppositedirections is the resultant signal-to-noise ratio (SNR) at the boundarybetween adjacent segments. It is known that in conventional recordingschemes, the noise is concentrated at the transition between oppositelypolarized segments. In particular, the media are noisiest whendemagnetized, as in the center of a transition in conventional binaryrecording schemes (see, for example, J. C. Mallinson, A New Theory ofRecording Media Noise, IEEE Trans. Magn., 27, pp 3519-3531, July, 1991).Noise power (NP) depends on the magnetic state as follows:

NP≈1−m ²;

[0014] where m=the magnetization (M) induced in a segment by the gapmagnetic field÷the remanent magnetization (M_(r)) of the segment. Thus,as shown on the graphs of FIGS. 4 and 5, the noise power (NP) will be ata maximum when the media is demagnetized (i.e., M=0). This state occurseach time transducing element transitions between a negatively andpositively polarized segment in conventional recording schemes.

[0015] The demagnetization which occurs with each segment transition inconventional recording has another disadvantage. According to thesuperparamagnetic effect, magnetic media formed of small grains tend todestabilize and lose their remanent magnetism in the presence of ademagnetizing field.

SUMMARY OF THE INVENTION

[0016] It is therefore an advantage of the present invention to storemore information in polarized segments on a magnetic storage disk incomparison to conventional recording systems.

[0017] It is another advantage of the present invention to magnetize asegment on a magnetic storage disk in a plurality of differentpolarization orientations.

[0018] It is another advantage of the present invention to reduce thelength of the transition region between adjacent segments.

[0019] It is a still further advantage of the present invention toreduce the signal-to-noise ratio at the transition between adjacentsegments.

[0020] It is another advantage of the present invention to increase thethermal stability of each segment by reducing the demagnetizing field atthe transition between adjacent segments.

[0021] These and other advantages are presented by the present inventionwhich in preferred embodiments relates to a method of storing andretrieving data to and from a magnetic disk wherein data maybe encodedon a data track in a large number of polarization orientations incomparison to conventional bidirectional recording schemes. In oneembodiment of the present invention, it is contemplated that a singlesegment may be polarized in eight different orientations, each of whichbeing distinguishable from each other by a read/write head. Polarizationof a segment in one of eight different orientations significantlyincreases the amount of information which can be stored in any givensegment relative to conventional systems which are polarized in only oneof two orientations. Thus, the amount of information which may be storedon a disk may be increased without having to alter the linear or radialdensity of the disk.

[0022] It is a further feature of the present invention that each of thepossible orientations in a preferred embodiment of the present inventionare directed down-track (i.e., no component of a polarization withineach segment in the X direction points in opposite directions). Thisfeature reduces the length of a boundary or transition region betweentwo adjacent segments. Moreover, having no X-component of adjacentsegments pointing in opposite directions, the signal-to-noise ratio atthe transition region is reduced in comparison to conventional recordeddata tracks having oppositely oriented polarized segments.

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The present invention will now be described with reference to thefigures in which:

[0024]FIG. 1 is a top view of a prior art data track including aplurality of oppositely polarized segments;

[0025]FIG. 2 is a perspective view of an azimuth recording systemaccording to the prior art;

[0026]FIG. 3 is an enlarged partial view of a boundary region of a priorart magnetic disk showing oppositely polarized domains;

[0027]FIG. 4 is a graph showing the induced magnetization withinadjacent, oppositely polarized segments on a data track;

[0028]FIG. 5 is a graph of a noise power at the transition regionbetween the segments shown in FIG. 4;

[0029]FIG. 6 is a top view of a head and disk assembly which may utilizethe multidirectional recording system according to the presentinvention;

[0030]FIG. 7 is a top view of a data track recorded according to themethod of the present invention including a plurality of differentlyoriented polarized segments;

[0031]FIG. 8 is a schematic representation of the segments shown in FIG.7 with the polarization of each segment broken down into X and Ycomponents;

[0032]FIG. 9 is an enlarged partial view of a transition region betweenadjacent segments of a magnetic disk recorded according to the method ofthe present invention;

[0033]FIG. 10 is a schematic representation of transducer elementscapable of polarizing a segment in any one of the desired orientationsduring a write process;

[0034]FIG. 11 is a graphic illustration of the current to be providedthrough the transducing elements shown in FIG. 10 for creating each ofthe segments shown in FIG. 7;

[0035]FIGS. 12 and 13 are schematic representations of transducerelements capable of polarizing a segment in any one of the desiredorientations during a write process according to alternative embodimentsof the present invention; and

[0036]FIGS. 14, 15 and 16 are schematic representations of threeconfigurations of magnetoresistive elements for reading the informationcontained within each of the segments recorded according to the methodof the present invention.

DETAILED DESCRIPTION

[0037] The present invention will now be described with reference toFIGS. 6-16 which in general relate to a system for storing andretrieving data to and from a magnetic disk wherein data may be encodedon a data track in a large number of polarization orientations incomparison to conventional bidirectional recording schemes. While thepresent invention is described with reference to a magnetic disk used ina Winchester-type hard disk drive, it is understood the method accordingto the present invention may be used to record data onto other magneticmedia, such as for example floppy disks and magnetic recording tape.Additionally, it is understood that the method according to the presentinvention may be utilized with various head technologies includingferrite metal in gap heads, inductive thin film heads andmagnetoresistive heads. It is also contemplated that the technique ofthe present invention may be used with optic or magneto-optic recordingtechnologies.

[0038] Referring now to FIG. 6, there is shown a top view of head anddisk assembly 100 including a read/write head 102 mounted on an actuatorassembly 104 over a magnetic disk 106. Head 102 includes a slider 108affixed to the actuator assembly 104, and a transducing element 110affixed to an end of slider 108. As is known in the art, upon rotationof disk 106, a cushion of air forces head 102 to “fly” over the disksurface so that data may be transferred between the transducing element110 and the disk 106. Data is written to and read from a plurality ofconcentric data tracks 112 (a portion of one of which is shown in thefigure) on disk 106.

[0039]FIG. 7 is a partial top view of a small portion of a data track112. Information is written onto data track 12 in a plurality ofcontiguous segments 114 by a transducing element 110 explained ingreater detail hereinafter. According to the present invention, thetransducing element is capable of writing data in the plurality ofcontiguous segments 114 by polarizing each segment in one of a pluralityof orientations. In the embodiment shown in FIG. 7, eight polarizationorientations are shown. It is however understood that the number ofpolarization orientations may be less than eight or greater than eightin alternative embodiments. In particular, the polarization orientationof each successive segment 114 shown in FIG. 7 is as follows:

[0040]114 ₁=0°

[0041]114 ₂=−45°

[0042]114 ₃=45°

[0043]114 ₄=90°

[0044]114 ₅=30°

[0045]114 ₆=−30°

[0046]114 ₇=−60°

[0047]114 ₈=60°

[0048] The angles set forth above with respect to the polarizationorientations are by way of example, and it is understood that variousother polarization orientations can be written into segments 114 bytransducer element 110.

[0049] As can be seen in the embodiment of in FIG. 7, each of thesegments 114 can be polarized in any one of eight differentorientations, with each orientation signifying a distinct and differentpiece of information. Thus, each segment 114 is capable of storingsignificantly more information in comparison to conventional binary datarecording schemes where a segment is polarized in only one of twoorientations. The amount, x, by which the information may bequantitatively increased within each segment 114 according to thepresent invention can be shown to conform to the relationship:

x=log₂ n;

[0050] where n is the number of different polarization orientations forthe particular embodiment of the invention. Therefore, for eightdifferent polarization orientations, the amount x by which theinformation within a segment 114 may be quantitatively increased is:

x=log₂ (8)

x=3

[0051] Thus, the embodiment illustrated in FIG. 7 is capable of storingthree times the data within a segment 114 than would a conventionalbinary recording system.

[0052] The recording method according to the present inventionpreferably has a lower aspect ratio in comparison to conventionalrecording systems. The aspect ratio refers to the ratio of a width of adata track (i.e., the dimension transverse to the direction of datatrack motion) relative to the length of a segment. In conventional diskdrives, this ratio is approximately 20:1. In a preferred embodiment ofthe present invention, the aspect ratio of the recording media isapproximately 1:1. The length of a polarized segment may be longer incomparison to that of conventional drives. However, as each segmentaccording to the present invention holds more information than those inconventional recording systems, the recording system of the presentinvention stores more information per unit length of data track thanconventional systems.

[0053] Referring now to FIG. 8, each of the segments 114 has apolarization orientation which may be broken down into an X-componentparallel to the direction of data track movement and a Y-componenttransverse to the direction of data track movement. In a preferredembodiment of the present invention, no X-component of the polarizationorientation of any given segment 114 is opposite that of any othersegment 114. With the exception of a segment polarized to 90° (as in 114₄), the X-component of each segment preferably faces in the samedirection. In the embodiment shown in FIG. 7, each of the segments (withthe exception of 114 ₄) has an X-component that faces down-track. It isunderstood that each of the segments may face up-track in alternativeembodiments.

[0054] As explained in the Background of the invention section, whereadjacent segments are polarized in completely opposite directions, as isconventional, the polarity or induced magnetism M must completelyreverse itself as the head transitions from one segment to the next.This transition must occur gradually, and as shown in FIG. 3 anddiscussed above, results in a relatively large transition length L₁.However, in the recording system of the present invention, as none ofthe polarization orientations have X-components facing opposite to eachother, a transition from one segment to the next never involves acomplete reversal of the polarity. Thus, as shown in FIG. 9, there is arelative small transition length, L₂ where the domains 116 have mixedpolarities.

[0055] Another advantage to the recording system according to thepresent invention is that the disk media is not completely demagnetizedwhen transitioning from one segment to the next. In particular, becauseadjacent segments will generally have X-components pointing in the samedirection, the polarization or induced magnetization within the mediawill generally not pass through a state where the magnetization goes tozero (where noise is at a maximum) in the transition region betweenadjacent segments. Thus, noise power NP is reduced and signal to noiseratio is improved relative to conventional recording schemes, which asdiscussed, involve a demagnetization when transitioning betweensegments.

[0056] A further advantage relating to the fact that the medium in thepresent invention is not completely demagnetized when transitioning fromone segment to the next is that the segments are more thermally stable.As indicated by the superparamagnetic effect, domains withinconventional systems are more likely to destabilize in comparison tothose of the present invention owing to the relatively strongerdemagnetizing fields which occur in conventional recording systems.

[0057] Although each of the segments have X-components of polarizationfacing in the same direction in a preferred embodiment, it is understoodthat the segments may be polarized to include oppositely facingX-components in alternative embodiments. While such embodiments may havewider transition regions between adjacent segments, each segment willcontain more information relative to conventional binary recordingsystems. In a further alternative embodiment of the present invention,it is contemplated that a segment can have two polarization orientationshaving at least an X-component facing in the same direction. While suchembodiments will be able to store only two states within each segment,the transition region between adjacent segments will be reduced relativeto conventional binary recording systems.

[0058] A transducer 110 for writing information onto the segments 114will now be described with reference to FIGS. 10 and 11. In order towrite segments in the plurality of orientations shown in FIG. 7, it isnecessary to employ at least two magnetic circuits. FIG. 10 illustratestwo magnetic circuits A and B, each including a pair of poles A1, A2 andB1, B2. Although not shown, the magnetic circuits further includeelectrical coils associated therewith for generating magnetic fieldsthat extend between poles A1, A2 and B1, B2. As would be appreciated bythose of skill in the art, the various polarization orientations may becreated in segments 114 by varying the amplitude and/or direction of thecurrent through the magnetic circuit coils. In particular, FIG. 11illustrates the current to be passed through magnetic circuits A and Bto create the various polarization orientations shown in FIG. 7. Graphs(1) through (8) correspond to segments 114 ₁ through ¹¹⁴ ₈,respectively. Thus, for example, current through circuits A and B asindicated in FIG. 11(2) will result in a magnetic field which polarizessegment 114 ₂ as shown in FIG. 7. By varying the current in one circuitrelative to the other circuit, one circuit will have a greater effect inestablishing the resultant magnetic field. For example, in FIG. 11(6),the current through circuit A is stronger than the current throughcircuit B. Thus, the resultant magnetic field and polarizationorientation is more closely aligned with an axis between poles A1, A2than an axis between poles B1, B2.

[0059] It is understood that the number of magnetic circuits utilizedmay vary in alternative embodiments. For example, FIG. 12 illustratesthree magnetic circuits A, B and C including six poles capable ofgenerating a plurality of polarization orientations in segments 114,depending on the amplitude and/or current through the respectivecircuits. The smallest number of poles which may be used to create theplurality of polarization orientations is three, as shown in FIG. 13.Additionally, it is understood that the orientation of the magneticcircuit core elements, with respect to both each other and the datatracks 112 over which they pass, may vary in alternative embodiments.

[0060]FIG. 13 also schematically illustrates the known technique ofthermally assisted recording. Where a disk has been fabricated topossess certain magnetic properties, the application of heat, as by alaser, to an area 118 on the disk being written will lower thecoercivity of the heated area. Lowering the coercivity allows thesegments to be polarized under a smaller applied magnetic field.According to an embodiment of the present invention, the areassurrounding area 118 are not heated, and as such do not receivesufficient applied magnetic field to become polarized. Thus, the laserin this embodiment may be controllably used along with the magneticcircuits to define the width of the data tracks polarized by the writehead. It is understood that the technique of thermally assistedrecording as described above may be used with any of the transducer 110configurations described above.

[0061] A read element for reading the information written in segments114 will now be described with reference to FIGS. 14 and 15. A readelement assembly 120 is provided including a plurality ofunidirectionally sensitive read elements mounted at an angle withrespect to each other. The read elements may be magnetoresistivetransducers, but it is understood that other read elements, such asinductive transducers, maybe utilized. Where inductive transducers areutilized, the same elements used to write information to the segments114 may be used to read the information. It is also contemplated thatthe technique of the present invention maybe used with optic ormagneto-optic recording technologies by using the longitudinal kerreffect readout.

[0062] The polarization orientation within a segment will generate amagnetic field which will affect the individual read elements of theassembly 120 differently, depending on the relative orientation of thesegment polarization to the elements of the assembly. Thus, referring toFIG. 14, the first pair of read elements are able to sense a firstcomponent of the magnetic field emanating from the segment 114, and thesecond pair of read elements are able to sense a second component of themagnetic field emanating from the segment 114. The intensity anddirection of the respective components detected by the read elements maythen be interpreted to determine orientation of the magnetic field inthe segment 114. Thus, each polarization orientation may bedistinguished and identified by the read element assembly. It iscontemplated that the assembly 120 may include four individual readelements (FIG. 14), or two individual read elements (FIG. 15). It isunderstood that various other numbers of read elements may be used, andthat the orientation of the read elements with respect to both eachother and the data tracks 112 over which they pass may vary inalternative embodiments.

[0063] The read assembly 120 shown in FIG. 16 is identical to that shownin FIG. 15, but is rotated 90°, for example, from that shown in FIG. 15.Rotating the assembly as show results in one of the read elements, i.e.,element 120 ₁, sensing a particular point over a segment before theother read element 120 ₂. The control circuit may however apply a clockdelay to element 120 ₂ so that it appears that the two elements are ineffect sensing the same point at the same time.

[0064] Although beyond the scope of the present invention, it isunderstood that the machine language used by the disk drive controlcircuitry would be tailored to transfer information to and from themagnetic disk according to the number of polarization orientationsutilized in that particular embodiment. In particular, where eightpossible polarization orientations are used, the machine language wouldoperate with number is base 8.

[0065] Although the invention has been described in detail herein, itshould be understood that the invention is not limited to theembodiments herein disclosed. Various changes, substitutions andmodifications may be made thereto by those skilled in the art withoutdeparting from the spirit or scope of the invention as described anddefined by the appended claims.

What is claimed is:
 1. A method of encoding information on a data trackof a magnetic storage medium, comprising the steps of: polarizing afirst segment on a data track in a first orientation, said firstorientation having at least one component substantially parallel to afirst axis, said first orientation being uniquely indicative of a firstitem of information; and polarizing a second segment on said data trackadjacent to said first segment in a second orientation, said secondorientation having at least one component substantially parallel to saidfirst axis; wherein said at least one component of said secondorientation is other and opposite said at least one component of saidfirst orientation.
 2. The method of encoding information described inclaim 1 wherein said step of polarizing a first segment comprises thestep of: applying a current to induce a magnetic field in said firstsegment of said magnetic storage medium.
 3. The method of encodinginformation described in claim 2 wherein said step of polarizing asecond segment comprises the step of: applying a current to induce amagnetic field in said second segment of said magnetic storage medium.4. The method of encoding information described in claim 1 wherein saidfirst axis is substantially tangential to said first segment of saiddata track.
 5. A method of reducing a transition boundary betweenadjacent segments on a magnetic medium, comprising the steps of:magnetizing a first segment of a magnetic storage medium in a firstorientation, said first orientation being indicative of a first item ofinformation, said first orientation having a first componentsubstantially parallel to a direction of travel or said magnetic medium;and magnetizing a second segment of said magnetic storage mediumadjacent to said first segment in a second orientation, said secondorientation being indicative of a second item of information, saidsecond orientation having a second component substantially parallel to adirection of travel of said magnetic medium.
 6. The method of encodinginformation described in claim 5 wherein said step of magnetizing afirst segment comprises the step of: applying a current to a transducerto induce a magnetic filed in said magnetic storage medium.
 7. Themethod of encoding information described in claim 6 wherein said step ofmagnetizing a second segment comprises the step of: applying a currentto a transducer to induce a magnetic filed in said magnetic storagemedium.
 8. The method of encoding information described in claim 5wherein said first component is substantially instantaneously tangentialto a portion of said first segment.
 9. A read/write apparatus forrecording data on a magnetic storage medium with a reduced transitionboundary between adjacent segments, comprising: a plurality ofmagnetizing elements for magnetizing segments of a magnetic storagemedium in a plurality of orientations; wherein adjacent segments aremagnetized such that at least one component of each magnetizationorientation of each magnetized segment is other an opposing at least onecomponent of magnetization orientations of adjacent magnetized segments.10. The read/write apparatus of claim 9, wherein said plurality ofmagnetizing elements are transducers.
 11. The read/write apparatus ofclaim 10, wherein said plurality of magnetizing elements includes atleast two transducers.
 12. The read/write apparatus of claim 9, whereineach said magnetizing element is oriented having a specific angularseparation relative to at least one adjacent magnetizing element.